1. Field of the Invention
The present invention relates to a magnetic recording medium. More particularly, it relates to a magnetic recording medium with improved durability comprising a magnetic layer containing hexagonal system ferrite powder as the magnetic powder.
2. Description of the Prior Arts
Conventionally, the magnetic properties of a magnetic recording medium has been improved, for example, by orientating longer axis of acicular particles of magnetic powder in the direction along a longitudinal direction of the magnetic layer. However, in the magnetic recording medium which utilizes magnetic components in the longitudinal direction of a magnetic layer, the strength of a diamagnetic field in the magnetic layer increases as the magnetic recording density increases. Therefore, the recording density has its own limitations.
In a perpendicular magnetic recording system which utilizes a magnetic component perpendicular to the plane of a magnetic layer, the strength of the demagnetizing field decreases as the recording density increases, so that such a recording system is recognized as being suitable for high density recording. As the most suitable magnetic powder for the perpendicular magnetic recording system, hexagonal system ferrite powder is used each particle of which has a platelet shape and magnetic easy axis in a direction perpendicular to said platelet plane (cf. Japanese Patent Kokai Publication (unexamined) No. 209928/1985).
However, the magnetic layer of a conventional magnetic recording medium, contains hexagonal system ferrite powder in a volume percentage of 42% or more based on the volume of the magnetic layer. Therefore, the amounts of a binder component which bonds the magnetic power to the substrate of an abrasive which reinforces the magnetic layer and of a lubricant which improves the lubricity of the surface of a magnetic powder is decreased, so that durability of the magnetic layer is not satisfactory.